Pyrene Monomer Emission Research Articles

Dipyrene-Terminated Oligosilanes Enable Ratiometric Fluorescence Response in Polymers toward Mechano- and Thermo-Stimuli

Developing fluorescent motifs capable of displaying mechano- and thermo-stimuli reversibly and ratiometrically is appealing for monitoring the deformation or temperature to which polymers are subjected. Here, a series of excimer-type chromophores Sin-Py (n = 1-3) consisting of two pyrenes linked with oligosilanes of one to three silicon atoms is developed as the fluorescent motif incorporated in a polymer. The fluorescence of Sin-Py is steered with the linker length where Si2-Py and Si3-Py with disilane and trisilane linkers display prominent excimer emission accompanied by pyrene monomer emission. Covalent incorporation of Si2-Py and Si3-Py in polyurethane gives fluorescent polymers PU-Si2-Py and PU-Si3-Py, respectively, where intramolecular pyrene excimers and corresponding combined emission of excimer and monomer are obtained. Polymer films of PU-Si2-Py and PU-Si3-Py display instant and reversible ratiometric fluorescence change during the uniaxial tensile test. The mechanochromic response arises from the reversible suppression of excimer formation during the mechanically induced separation of the pyrene moieties and relaxation. Furthermore, PU-Si2-Py and PU-Si3-Py show thermochromic response toward temperature, and the inflection point from the ratiometric emission as a function of temperature gives an indication of the glass transition temperature (Tg) of the polymers. The design of the excimer-based mechanophore with oligosilane provides a generally implementable way to develop mechano- and thermo-dual-responsive polymers.

Synthesis and Photophysical Properties of Light-Harvesting Gold Nanoclusters Fully Functionalized with Antenna Chromophores.

The development of efficient light-harvesting systems is important to understand the key aspects of solar-energy conversion processes and to utilize them in various photonic applications. Here, atomically well-defined gold nanoclusters are reported as a new platform to fabricate artificial light-harvesting systems. An efficient amide coupling method is developed to synthesize water-soluble Au22 clusters fully protected with pyrene chromophores by taking advantage of their facile phase-transfer reaction. The synthesized Au22 clusters with densely packed 18 pyrene chromophores (Au22 -PyB18 ) exhibit triple-emission in blue, green, and red wavelength regions arising respectively from pyrene monomer, pyrene excimer, and Au22 emission, producing bright white light emission together. The photoluminescence of Au22 is enhanced by more than tenfold, demonstrating that pyrenes at the periphery efficiently channel the absorbed energy to the luminescent Au22 at the center. A combination of femtosecond transient absorption and anisotropy measurements of Au22 -PyB18 explicitly reveals three main decay components of 220 fs, 3.5ps, and 160ps that can be assigned to energy migration between pyrenes and energy transfer processes from pyrene monomer and excimer to the central Au22 , respectively.

Alkynylated and Dendronized 5-Aza-7-deazaguanine Nucleosides: Cross-Coupling with Tripropargylamine and Linear Alkynes, Click Functionalization, and Fluorescence of Pyrene Adducts†.

The change of the recognition face of 5-aza-7-deazaguanine bridgehead nucleosides with respect to purine nucleosides permits the construction of new purine-purine or purine-pyrimidine base pairs in DNA and RNA. Clickable derivatives of 5-aza-7-deazaguanine were synthesized by introducing ethynyl, 1,7-octadiynyl, and tripropargylamino side chains in the 7-position of the 5-aza-7-deazapurine moiety by Sonogashira cross-coupling. Click reactions were performed with 1-azidomethylpyrene by the copper-catalyzed azide-alkyne cycloaddition. The copper(I)-catalyzed click reaction on the tripropargylamino nucleoside was significantly faster and higher yielding than that for nucleosides carrying linear alkynyl chains. Also, this reaction could be performed with copper(II) as the catalyst. An autocatalyzed cycle was suggested in which the click product acts as a catalyst. Pyrene click adducts of linear alkynylated nucleosides showed pyrene monomer emission, while tripropargylamino adducts showed monomer and excimer fluorescence. The fluorescence intensities of the 5-aza-7-deazaguanine nucleosides were higher than those of their 7-deazaguanine counterparts. The reported clickable nucleosides can be utilized to functionalize or to cross-link monomeric nucleosides or DNA for diagnostic or imaging purposes and other applications in nucleic acid chemistry and biotechnology.

Highly sensitive pyrene–dansyl conjugate-based fluorescent sensor for discriminative detection of water in organic solvents

In this work, we designed a dual-fluorophore-based water sensor 5-(dimethylamino)- N'-(pyren-1-ylmethylene)naphthalene-1-sulfonohydrazide (PDH) by combining pyrene, which exhibits monomer/excimer switching emission, and dansyl, which shows typical intramolecular charge transfer (ICT) activity. The effects of solvents on PDH and two control compounds were studied. Results showed that PDH exhibited tunable fluorescence properties, and the two fluorescent units of PDH could behave independently and synergistically. Generally, the fluorescent emission of PDH displayed two distinct modes in various solvents. On the one hand, only pyrene emission was observed in N, N-dimethylformamide (DMF), acetonitrile (AN), ethanol (EtOH), dimethyl sulfoxide (DMSO), methanol (MeOH), acetone, and tetrahydrofuran (THF) because these solvents affected the push–pull interactions between dimethyamino moiety and naphthalenesulfonyl and the aggregation behavior. On the other hand, efficient Förster resonance energy transfer (FRET) from the pyrene unit to the dansyl moiety was observed in dichloromethane (CH2Cl2), chloroform (CHCl3), ethyl acetate (EA), toluene, and water (H2O). The fluorescence spectra displayed strong dansyl emission and weak pyrene monomer emission due to the synergy of ICT and FRET. By taking advantage of the monomer/excimer switching, ICT, and FRET activities, the fluorescence tunability of PDH was applied for the differentiation of solvents and discriminative detection of H2O content in three organic solvents, including acetone, DMF, and DMSO.

A simple triazole-linked bispyrenyl-based xylofuranose derivative for selective and sensitive fluorometric detection of Cu2+

Triazole-linked xylofuranose derivatives having one pyrene or two pyrene moieties were synthesized and their fluorescence properties towards various cations and anions were investigated. Only, bis-triazoles appended bispyrenyl-based sugar derivative 1 exhibited selective and sensitive fluorescence quenching effect in the presence of Cu2+ ions over a wide range of cations and anions in acetonitrile. The ON-OFF type fluorescence response of 1 was explained by the conformational changes from strong excimer emission of pyrene to weak pyrene monomer emission due to an interaction between Cu2+ and inward-facing triazole groups. The limit of detection (LOD) of sensor 1 for Cu2+ was found to be 0.15 µM, which is well accepted as per WHO’s guidelines.

Pyrene-Functionalized Polyacetylenes: Synthesis and Photoluminescence Property.

Four pyrene-functionalized polyacetylenes were designed and prepared through a typical post-polymerization modification route, which is the highly efficient reaction between activated ester and primary anime groups. The chemical structures of the resultant polymers were characterized with multiple spectroscopic techniques and the data indicated the successful functionalization of the polyacetylenes. The introduction of the pyrene moieties into the polymer structure allowed us to investigate the interactions between the polymer backbone and side chains. For the mono-substituted polyacetylenes, both the monomer and excimer emission features of the pyrene groups could be recorded, while for the di-substituted polyacetylenes, the fluorescence from the pyrene excimer vanished and the fluorescence intensity from the pyrene monomer decreased, the fluorescence from the polymer chain predominated the emission features. The concomitant energy transfer from the pyrene monomer and excimer to poly(diphenylacetylene) backbone was associated with the underlying mechanism. In addition to the substitution modes, the linkage between the poly(diphenylacetylene) backbone and the pyrene moiety also played a significant role in the determination of the emission species. A long alkyl spacer was beneficial to the pyrene monomer emission while a short one may be helpful to the formation of the excimer and intramolecular energy transfer.

Thiazoline-pyrene selective and sensitive fluorescence "turn-on" sensor for detection of Cu2.

A thiazoline and pyrene containing sensor 1 was synthesized via one-pot reaction and utilized as a highly selective and sensitive fluorescence "turn-on" sensor for Cu2+ detection, via the fluorescence enhancement of pyrene monomer emission. The 2:1 stoichiometry of 1 and Cu2+ was calculated from Job's plots based on fluorescent titrations, and the complexation of 1 with Cu2+ was also supported by mass spectra, Fourier transform infrared spectra, proton NMR spectra and density functional theory analysis. The fluorescence intensity of 1 at 389 nm and 410 nm increased significantly upon the addition of Cu2+. Limit of detection and association constant value of 1-Cu2+ were calculated using standard deviations and linear fittings, respectively. Results showed that 1 was active for Cu2+ detection in the wide pH range of 2.0-11.0.

Design of novel well-defined oligothiophenes bearing donor-acceptor groups (pyrene-porphyrin): Synthesis, characterization, optical properties and energy transfer

Novel thiophene monomers containing porphyrin units attached via di(ethylene glycol) and tetra(ethylene glycol) spacers were synthesized: 3-methyl-4- (4- (1- (5-phenyl-10,15,20-triphenylporphyrin)) diethoxy) thiophene (M2PPh) and 3-methyl-4- (4- (1- (5-phenyl-10,15,20-triphenylporphyrin)) tetraethoxy) thiophene (M4PPh). These monomers and other co-monomers with pyrene units 3-methyl-4-(diethoxy) thiophene (M2) and 3-methyl-4-(tetraethoxy) thiophene (M4) previously reported by us, were linked to thiophene and bithiophene via a Suzuki coupling reaction to give the corresponding terthiophenes and quaterthiophenes: [3-diethoxypyrene, 3-diethoxyporphyrin, 4,4‴ dimethyl - 2,2: 5′2”- terthiophene (TT2PY-PPh)], [3-tetraethoxypyrene, 3-tetraethoxyporphyrin, 4, 4‴dimethyl - 2,2:5′2”-terthiophene (TT4PY-PPh)], [3′-diethoxypyrene, 3′-diethoxyporphyrin, 4,4‴methyl-2,2′:5′: 2′′:5″,2‴-quaterthiophene (QT2PY-PPh)], and [3′-tetraethoxypyrene, 3′-tetraethoxyporphyrin,4,4‴methyl −2,2′:5′:2′′:5″,2‴-quaterthiophene (QT4PY-PPh)]. The synthesized compounds were characterized by 1H NMR, 13C NMR and MALDI-TOF mass spectrometry; their optical properties were studied by absorption and fluorescence spectroscopy. The emission spectra of the oligothiophenes bearing pyrene-porphyrin units showed a significant decrease in the pyrene monomer emission and the appearance of a new emission band at 650 nm, arising from the porphyrin, which revealed that a FRET phenomenon is occurring from the excited pyrene to the porphyrin. The obtained FRET efficiencies were between 93 and 98% depending on the oligomer structure.

Rapid Identification of Bacteria by Membrane-Responsive Aggregation of a Pyrene Derivative.

An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species. When the nonemissive aggregates bound to the anionic bacteria surface, the sensor disassembled to turn on significant fluorescence. At the same time, ratiometric signals between pyrene monomer and excimer emission were controlled by different interactions with various bacteria surfaces. The resulted different fluorescent emission profiles then were obtained as fingerprints for various bacterial species. By converting emission profiles directly into output signals of two channels, fluorescence increase and ratiometric change, a two-dimensional analysis map was generated for bacteria identification. We demonstrated that our sensor rapidly identified 10 species of bacteria and 14 clinical isolated multidrug-resistant bacteria, and we determined their staining properties (Gram-positive or Gram-negative).

Monitoring the confinement of methylene blue in pyrene labeled poly(acrylic acid)

This work was devoted to investigate the aggregation of methylene blue (MB) with pyrene labeled poly(acrylic acid) (PAA25Py3) by using the measurements of UV–vis absorption, steady-state and time-resolved fluorescence. For comparison, the effect of unlabeled poly(acrylic acid) (PAA25) on the self-association of MB was also evaluated. The spectral positions of the absorption and emission bands of MB as well as the pyrene monomer and excimer emissions were used to assess the local changes of polymer/MB microenvironment. The binding mechanism and thermodynamic analysis for the interaction between MB and pyrene labeled poly(acrylic acid) were evaluated by fluorescence quenching measurements. Moreover, the strategy of switching of pyrene excimer/monomer emission was used to manage the self-aggregation of the pH-responsive fluorescent polymer with phenothiazinium dye. The UV–vis absorption and fluorescence results showed that low amounts of polymers provoked the self-association of MB. At high concentrations of polymer, the MB monomer is stabilized. The labeling of polymer with pyrene induced a dramatic changing of optical properties suggesting that a peculiar process occurred between PAA25Py3 and MB. At low quencher concentrations, both steady-state and time-resolved fluorescence data indicated a static quenching process. The thermodynamic parameters (∆H, ∆S and ∆G) and the efficiency of pyrene excimer formation revealed that the association of MB with the fluorescent polymer occurred spontaneously due to non-covalent hetero π-π stacking, hydrophobic and electrostatic interactions. The study highlights the key contribution of the π-π stacking interactions in the capturing of methylene blue in pyrene labeled poly(acrylic acid). The outcome may be useful in biomedical applications or in wastewater treatment.

Pyrene‐functional star polymers as fluorescent probes for nitrophenolic compounds

ABSTRACTNovel tetra‐armed star‐shaped styrenic copolymers with pyrene side groups [(S1‐S3)‐Pyr] were prepared and employed as fluorescence sensing probe for fast and sensitive determination of nitroaromatic compounds. (S1‐S3)‐Pyr depicted characteristic pyrene monomer emission signals as well as broad excimer bands in their fluorescence emission spectra due to close proximity of the pyrene groups on the polymer chains and the ratio of monomer to excimer emission intensities gradually decreased as the pyrene content of the star polymers were increased from S1‐Pyr to S3‐Pyr. The highest quenching efficiency in the presence of 25 equivalent nitroaromatics was observed for 2,4,6‐trinitrophenol/picric acid (99.4%) followed by 2,4‐dinitrophenol (84.2%), 4‐nitrophenol (82.6%), 2,4,6‐trinitrotoluene (44.0%), 2,4‐dinitrotolunene (32.6%), and 4‐nitrotoluene (28.8%). Superior quenching efficiencies of nitrophenolic compounds were ascribed to their strong binding affinity for (S1‐S3)‐Pyr due to the acidity of phenolic hydroxyl units. Besides, quenching ratios of S1‐Pyr, S2‐Pyr, and S3‐Pyr were measured to be very close to each other. Thus, (S1‐S3)‐Pyr are considered to be highly selective and sensitive fluorescence probes for phenolic nitroaromatic compounds. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46310.

Bis(1-pyrenylmethyl)-2-benzyl-2-methyl-malonate as a Cu2+ Ion-Selective Fluoroionophore.

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λem = 467 nm) emissions and not a pyrene monomer emission (λem = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (ΦPL = 0.65) rather than in solution (ΦPL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C–H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu2+ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu2+ ion.

Factors influencing the aggregation behavior of residual associative polymer in produced oily fluids

The influence of emulsified oil, suspended solids, Fe3+, Fe2+, cationic water clarifier and sulfate-reducing (SR) bacteria on the aggregation behavior of residual hydrophobic modified polyacrylamide in treated oily wastewater from polymer flooding was studied by fluorescence spectroscopy and dynamic light scattering. The result of I1/I3 showed that the polarity of hydrophobic microdomains increased, whereas the size of the hydrophobic microdomains may be decreased, where the value of I1/I3 represents the ratio of the intensity of peak I1 (374.0 nm) to that of peak I3 (385.0 nm) of the vibration fine structure of pyrene monomer emission in residual polymer solution. The results of the ratio of I1 at 48 h to I1 at 0 h (I1,48h/I1,0h) indicated that oil and cationic water clarifier could inhibit the aggregation to some extent, while Fe2+ and suspended solids were helpful for aggregation, and Fe3+ and SR bacteria had no significant influence on the aggregation of polymer.

Membrane Binding and Oligomerization of the Lipopeptide A54145 Studied by Pyrene Fluorescence

A54145 is a lipopeptide antibiotic related to daptomycin that permeabilizes bacterial cell membranes. Its action requires both calcium and phosphatidylglycerol in the target membrane, and it is accompanied by the formation of membrane-associated oligomers. We here probed the interaction of A54145 with model membranes composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol, using the steady-state and time-resolved fluorescence of a pyrene-labeled derivative (Py-A54145). In solution, the labeled peptide was found to exist as a monomer. Its membrane interaction occurred in two stages that could be clearly distinguished by varying the calcium concentration. In the first stage, which was observed between 0.15 and 1 mM calcium, Py-A54145 bound to the membrane, as indicated by a strong increase in pyrene monomer emission. At the same calcium concentration, excimer emission increased also, suggesting that Py-A54145 had oligomerized. A global analysis of the time-resolved pyrene monomer and excimer fluorescence confirmed that Py-A54145 forms oligomers quantitatively and concomitantly with membrane binding. When calcium was raised beyond 1 mM, a distinct second transition was observed that may correspond to a doubling of the number of oligomer subunits. The collective findings confirm and extend our understanding of the action mode of A54145 and daptomycin.

Fluorescent Peptide Beacons for the Selective Ratiometric Detection of Heparin.

Heparin is extensively used as an anticoagulant drug during surgery. Two fluorophore-functionalized cationic oligopeptides HS 1 and HS 2 were developed to monitor heparin ratiometrically in aqueous media. Upon binding to heparin, HS 1 and HS 2 undergo a conformational change from an open form to a folded form, which leads to a distinct change in the fluorescence properties. HS 1 switches from pyrene monomer emission to an excimer emission. For HS 2, a fluorescence resonance energy transfer (FRET) process is enabled between a naphthalene donor and a dansyl acceptor. This method is highly selective for heparin relative to other similar biological analytes such as hyaluronic acid or chondroitin sulfate. HS 1 and HS 2 could also detect heparin ratiometrically in diluted bovine serum. The strong ratiometric emission color change can also be observed by the naked eye. Addition of the polycationic protein protamine releases both HS 1 and HS 2 from their heparin complex, which simultaneously restores pyrene monomer emission for the first case and decreases the FRET process for the latter case, respectively. Dynamic light scattering (DLS) and AFM studies confirm aggregate formation of heparin with HS 1 and HS 2.

Pyrene bisiminopyridine ligand and its zinc complex

ABSTRACTThe synthesis of a pyrene bisiminopyridine ligand L was successfully accomplished by condensation between 1-aminopyrene and 2,6-pyridinecarboxaldehyde. The complexation of L with zinc triflate afforded a neutral metal complex formulated as [Zn(H2O)LCF3SO3)2].2Et2O. In the complex, the ligand is coordinated to zinc(II) through its three nitrogen atoms which form a distorted octahedral environment together with three oxygen atoms, two from the triflate anions and one from aqua ligand. Both compounds have been characterized using NMR, elemental analysis, mass spectrometry, electronic absorption (UV-Vis) and infrared. Luminescence properties of these compounds show an emission maxima at 412 nm, indicating a pyrene monomer emission.

Synthesis, Characterization, and Ion Sensing Application of Pyrene‐Containing Chemical Probes

A novel pyrene‐functionalized thiophene compound (Thi‐Pyr) and pyrene‐functionalized styrene polymers (P7–9) are synthesized via 1,3‐dipolar cycloaddition reaction between the azide functional groups of the precursors and 1‐ethynylpyrene. Glass transition temperature of the styrene polymers increases remarkably upon the covalent attachment of the pyrene unit through triazole linkers, whereas the thermal stabilities of the styrene polymers are not affected by the incorporation of pyrene moieties. Thi‐Pyr exhibits the characteristic pyrene monomer emission bands; on the other hand, P7–9 show the excimer emission bands of pyrene due to the excitation of ground state dimeric species. The monomer emissions of Thi‐Pyr and the excimer emissions of P7–9 are distinguishably increased by the addition of HP2O73−, Cl−, and Br− anions. The responses of Thi‐Pyr and P7–9 to the addition of HP2O73− are stronger than any other anions, indicating their selectivity to HP2O73− anion to some extent. image

Fluorescent peptide-based sensors for the ratiometric detection of nanomolar concentration of heparin in aqueous solutions and in serum

New fluorescent peptide-based sensors (1–3) for monitoring heparin in serum sample were synthesized using short peptides (1∼3mer) as a receptor. The peptide-based sensors (2 and 3) showed a sensitive ratiometric response to heparin both in aqueous buffered solution (10mM HEPES, pH 7.4) and in 2% human serum sample by increase of excimer emission of pyrene at 480nm and concomitant decrease of monomer emission of pyrene at 376nm, whereas the peptide-based sensor 1 showed a turn off response only by decrease of monomer emission at 376nm. 2 and 3 exhibited excellent selectivity toward heparin among various anions and competitors of heparin including chondroitin 4-sulfate (ChS) and hyaluronic acid (HA). Peptide-based sensor 3 showed a more sensitive response to heparin than 2. The detection limit of 3 was determined as 36pM (R2=0.998) for heparin in aqueous solution and 204pM (R2=0.999) for heparin in aqueous solutions containing 2% human serum. The peptide-based sensors, 2 and 3 provided a practical and potential tool for the detection and quantification of heparin in real biological samples.

Bis-pyrene-modified unlocked nucleic acids: synthesis, hybridization studies, and fluorescent properties.

Efficient synthesis of a building block for the incorporation of a bis-pyrene-modified unlocked nucleic acid (UNA) into oligonucleotides (DNA*) was developed. The presence of bis-pyrene-modified UNA within a duplex leads to duplex destabilization that is more profound in DNA*/RNA and less distinct in DNA*/DNA duplexes. Nevertheless, the destabilization effect of bis-pyrene-modified UNA is weaker than that of unmodified UNA. Some oligonucleotides with bis-pyrene-modified UNA incorporations displayed superior mismatch discrimination capabilities. UV/Vis absorption and molecular modeling studies indicate that the pyrene groups of bis-pyrene-modified UNA are located in the major groove of a duplex. Oligonucleotides containing two bis-pyrene-modified UNA monomers showed low pyrene monomer emission in bulge-containing duplexes, high pyrene monomer emission in fully matched duplexes, and 5-(pyrenyl)uracil:pyrene exciplex emission in the single-stranded form. Such fluorescent properties enable the application of bis-pyrene-modified UNA in the development of fluorescence probes for DNA/RNA detection and for detection of deletions at specific positions.

Fluorescence of pyrene in inhomogeneous media containing silver nanoparticles

Pyrene fluorescence in inhomogeneous media based on ionic detergents containing silver nanoparticles with different morphologies is investigated. An increase in pyrene monomer emissions in the spectral range of 400–500 nm is observed, due to the resonance between electronic transitions in pyrene molecules in that region and the plasmonic oscillations of silver nanoparticles.